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Suburban Temperature Gauge Pegged

Mickey_Spiers

By Mickey_Spiers
in Ask A GM Technician

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Mickey_Spiers Enthusiast

Mickey_Spiers

Posted
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I have a 1998 GMC 2500 Suburban with a 454, A/C, no AIR pump. At 100,054 miles, the bearings in the water pump disentegrated. This caused the serpentine belt to derail and fly off - fun stopping with no power brakes or steering (a drawback to a hydraulic brake system). Anyway, the truck completely overheated before I could pull it over (middle of nowhere in eastern Colorado during a snowstorm and not many exits) and basically drained the block of all coolant through the nose of the water pump in the form of a giant steaming disaster. 120 miles on a flatbed later, a quick check showed that even after sitting for two weeks the temperature gauge was still pegged. No hoses had burst. I've replaced the water pump and the temperature sensor (and the hoses & belt since I was in there), filled back up with DexCool; the truck started right up, seems to run OK (it has a slight stumble which is new, but pulled fine when I accelerated) and doesn't look to leak anything, but I've not driven it much at all as the gauge is still pegged. What else did I fry? I've found no water in the oil (Mobil 1 if it matters) nor oil in the water, but again I've only driven it a half mile in my neighborhood before shutting it down for fear of doing further damage. Any ideas would be appreciated.

 

-Mickey

grampadirt Senior Enthusiast

grampadirt

Posted
Posted
I have a 1998 GMC 2500 Suburban with a 454, A/C, no AIR pump. At 100,054 miles, the bearings in the water pump disentegrated. This caused the serpentine belt to derail and fly off - fun stopping with no power brakes or steering (a drawback to a hydraulic brake system). Anyway, the truck completely overheated before I could pull it over (middle of nowhere in eastern Colorado during a snowstorm and not many exits) and basically drained the block of all coolant through the nose of the water pump in the form of a giant steaming disaster. 120 miles on a flatbed later, a quick check showed that even after sitting for two weeks the temperature gauge was still pegged. No hoses had burst. I've replaced the water pump and the temperature sensor (and the hoses & belt since I was in there), filled back up with DexCool; the truck started right up, seems to run OK (it has a slight stumble which is new, but pulled fine when I accelerated) and doesn't look to leak anything, but I've not driven it much at all as the gauge is still pegged. What else did I fry? I've found no water in the oil (Mobil 1 if it matters) nor oil in the water, but again I've only driven it a half mile in my neighborhood before shutting it down for fear of doing further damage. Any ideas would be appreciated.

 

-Mickey

 

My 95 has 2 sensors,maybe yours does too,did you check both?Same location on the other side of the engine......

Mickey_Spiers Enthusiast

Mickey_Spiers

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My 95 has 2 sensors,maybe yours does too,did you check both?Same location on the other side of the engine......

 

I only saw one, which was centered on the front of the motor, right at the top radiator hose at the intake manifold, smack on top of the water pump itself. Are yours different? Do you have one in the rear? I'd think your '95 has the same 7.4L that I do. My Chilton's only mentions one for all big blocks so I'm obviously missing something.

redvett Senior Enthusiast

redvett

Posted
Posted

The CTS is the one with a yellow & black pair of wires that go to the PCM the guage sender is a one wire with a green wire that only goes to the cluster. If you have no SES light the engine isnt overheating. I recall the SES will come on at about 247-250F. Yo9u can have someone a use a data scanner and read PCM coolant data its more accurate then the guage.

redvett Senior Enthusiast

redvett

Posted
Posted

SES is the service engine soon. If it didnt come on the engine never got to 247F i would replace the guage sender. Does the SES light come on when engine is not running and ign. is on?

 

Sorry, what does SES stand for? The only light on the dash is the one that tells me to check the gauges. That's also the only light that came on when the water pump let loose.
Mickey_Spiers Enthusiast

Mickey_Spiers

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SES is the service engine soon. If it didnt come on the engine never got to 247F i would replace the guage sender. Does the SES light come on when engine is not running and ign. is on?

 

Ah, thank you. Yes, Service Engine Soon is on when ignition is on with no motor running. Crank it up, all lights go out except Check Gages.

 

I looked at the sensor I replaced - it is on the intake manifold below the water inlet above the water pump, and has two wires: a greenish/yellow wire and a black one. The only other obvious sensor/sender I found was on the head, just above the exhaust manifold on the left (drivers) side about right in the middle. This had a single purple wire going to it.

 

I also stopped by NAPA to ask for another sender/sensor, figuring I could track down by looks whatever they sold me. They list the same part number for both the gage and the computer, but weren't sure if this meant it took two of the same sensors or if the one sensor did both functions.

redvett Senior Enthusiast

redvett

Posted
Posted

The sender on the cyl. head is the guage your NAPA is on the wrong Platform you have a GMT400 & he is on the GMT800 all GMT800's use the CTS for both the PCM & cluster.

 

SES is the service engine soon. If it didnt come on the engine never got to 247F i would replace the guage sender. Does the SES light come on when engine is not running and ign. is on?

 

Ah, thank you. Yes, Service Engine Soon is on when ignition is on with no motor running. Crank it up, all lights go out except Check Gages.

 

I looked at the sensor I replaced - it is on the intake manifold below the water inlet above the water pump, and has two wires: a greenish/yellow wire and a black one. The only other obvious sensor/sender I found was on the head, just above the exhaust manifold on the left (drivers) side about right in the middle. This had a single purple wire going to it.

 

I also stopped by NAPA to ask for another sender/sensor, figuring I could track down by looks whatever they sold me. They list the same part number for both the gage and the computer, but weren't sure if this meant it took two of the same sensors or if the one sensor did both functions.

 

Mickey_Spiers Enthusiast

Mickey_Spiers

Posted
  • Author
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Alright, that was the one. I hopped on the online NAPA catalogue, found a temperature "switch" that was for the gage, and that got everything back to normal. Thanks so much for the help!

 

-Mickey

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